The present invention generally relates a threaded inner sleeve for a magnetized rotor for the motor or generator and, more specifically, to a threaded inner sleeve that may apply an axial compressive force onto the magnet.
Permanent magnet rotors are frequently used in dynamo electric machines such as motors and generators. Permanent magnets are secured to a rotor hub or shaft by any of a variety of means and care must be taken to assure that such securement prevents the magnets from moving either axially or radially. If axial movement is permitted, one or more magnets may not properly align with an armature with the consequence that machine efficiency diminishes. If radial movement occurs, the probability of interfering contact between the rotor and the stator, and the resulting frictional drag and/or damage to machine parts come into existence.
Conventional motor or generator designs may use any shape magnet, so long as a hole is formed in the center of the magnet(s) for insertion of a rotor. As an example, and referring to FIG. 1, arc-shaped magnet sections 10 may be arranged to form a donut shape. A rotor shaft 12 may be inserted in the hole of the donut shape magnet. An outer ring 14, sized slightly smaller than the donut shape of magnet sections 10, is heated to cause its thermal expansion, allowing outer ring 14 to fit around an outside edge 16 of magnet sections 10. Upon cooling, radial shrinkage due to the thermal coefficient of expansion of metal outer ring 14 holds magnet sections 10 frictionally in place.
These conventional motor and generator configuration assembly methods are complex and result in high initial manufacturing costs as well as high operational costs. Manufacturing costs are high due to the need for a close tolerance between outside edge 16 of magnet sections 10 and outer ring 14, requiring machining of both outer ring 14 and magnet sections 10 to exacting standards. Operational costs are high due to possible rotor slippage and/or magnet cracking under operating conditions.
U.S. Pat. No. 4,433,261 concerns a structure for attaching magnets of a rotor for a synchronous motor of a permanent magnet type. Side plates (4) are fixed on a rotor shaft (2). Grooves (4a) are formed in side plates (4). Grooves (4a) match the size of one of the arc-shaped sections of magnet (1). Therefore, one magnet section (1) will fit into groove (4a) and the adjacent magnet section (1) will be offset, fitting into a corresponding groove (4a) of the opposite side wall (4). This configuration forces magnet (1) to move with rotor shaft (2), since side walls (4) are fixed to rotor shaft (2) (FIGS. 3 and 4). This conventional configuration requires the use of magnet segments that are specifically sized to fit into grooves (4a). Should the magnet size or shape change, side plates (4) must be milled to different grooves (4a) to match this size change. Moreover, grooves (4a) must be milled to fairly close size standards to match the size of magnet sections (1).
As can be seen, there is a need for a motor or generator configuration wherein the magnet is contained or fixed in position on the rotor shaft, especially during the machine's worst operating conditions. Such a configuration should be simple in design and relatively low cost in its manufacture.